In the prior art, the patent document of CN 101885110A discloses a rotational position detecting device, which adopts two rotators with different periods of rotation. The rotators are provided with one or more claws and provided with corresponding claw sensors so as to detect the rotation number and rotation angle. As a result of providing multiple rotators, the manufacturing costs of the detecting device are increased, and a increased components in turn raise the costs for adjustment and maintenance inevitably.